In order to detect an underwater vehicle and so on, for example, in Japanese Patent Application Laid-Open No. 1995-318660, Japanese Patent Application Laid-Open No. 2001-287694 and Japanese Patent Application Laid-Open No. 1991-282390, a technology using a sensor such as a sonar or a magnetic detector is disclosed. In this technology, the sensor is fixedly installed or loaded on a warship. And by operating the sensor to follow the underwater vehicle, the position of the underwater vehicle is detected successively. Or by using a plurality of sensors, the position of the underwater vehicle is detected successively.
FIG. 9 is a schematic diagram showing a detection method of such the underwater vehicle. Sensor 1 such as sonar or a magnetic detector is installed on the warship or a helicopter 3a and so on, fixed at the bottom of the sea, or thrown into the bottom of the sea from the warship or the helicopter 3b and so on, and detects the underwater vehicle. The detection range of sensor 1 is a predetermined range with the position of the sensor itself as the center. Because the detection range of sensor 1 is limited as mentioned above, it is not possible to detect the underwater vehicle successively by an acoustic sensor such as a fixed sensor located at the bottom of the sea, or the sonar which is mounted on the warship or an airplane. Accordingly, in order to successively detect a position of moving underwater vehicle 5, it is necessary to detect the underwater vehicle 5 continually by the moving sensor 1 following the underwater vehicle 5 or by using a plurality of the sensors 1-1, 1-2 . . . 1-8.
However, when the underwater vehicle is detected successively or intermittently by the moving sensor 1 following the underwater vehicle 5 or by using a plurality of the sensors, propagation condition of sound and so on changes depending on the environmental condition in the water, and it is difficult to keep detecting it stably for a long time.
Also, even if the underwater vehicle can be detected, without the sensor following the detected underwater vehicle or without installing a large number of sensors, it is not possible to detect the position of a mother ship which starts this underwater vehicle or to which it returns. Accordingly, an organization and so on for which the underwater vehicle or the mother ship belongs to cannot be grasped sufficiently.
Also, as the sensor performs position detection only, when the distance between the detected underwater vehicle or the mother ship and the warship and so on which loads the sensor is far, it is not possible to inhibit the movement of the detected underwater vehicle or the mother ship.
Also, because the underwater vehicle 5 cannot perform a long time or a long distance operation independently, possibility that it returns to the mother ship 2 which started it is high. However, even if the underwater vehicle or the mother ship 2 can be detected by the sensor 1, as far as these relations cannot be detected.